A “gamechanger” immunotherapy drug that “melts away” tumours dramatically increases the chances of curing bowel cancer and may even replace the need for surgery, doctors have said. Pembrolizumab targets and blocks a specific protein on the surface of immune cells that then seek out and destroy cancer cells. Giving the drug before surgery instead of chemotherapy led to a huge increase in patients being declared cancer-free, a clinical trial found. The results were presented at the annual meeting of the American Society of Clinical Oncology (ASCO), the world’s largest cancer conference. The study was led by University College London, University College London hospital, the Christie NHS Foundation Trust in Manchester, St James’s University hospital in Leeds, University hospital Southampton and the University of Glasgow. Prof Mark Saunders, a consultant clinical oncologist at the Christie, said the trial results were “really very exciting”. “Immunotherapy prior to surgery could well become a ‘gamechanger’ for these patients with this type of cancer. Not only is the outcome better, but it saves patients from having more conventional chemotherapy, which often has more side-effects. In the future, immunotherapy may even replace the need for surgery.” Bowel cancer is the second leading cause of cancer-related deaths worldwide. There are more than 1.9m new cases and more than 900,000 deaths a year, according to the World Health Organization. In the trial, funded by Merck Sharp and Dohme and sponsored by University College London, researchers recruited 32 patients with stage two or three bowel cancer and a certain genetic profile (MMR deficient/MSI-High bowel cancer) from five hospitals in the UK. About 15% of patients with stage two or three bowel cancer have this particular genetic makeup. Patients were given nine weeks of pembrolizumab, also known as Keytruda, before surgery instead of the usual treatment of chemotherapy and surgery, then monitored over time. Results show 59% of patients had no signs of cancer after treatment with pembrolizumab, with any cancer in the remaining 41% of patients removed during surgery. All of the patients in the trial were cancer-free after treatment. When standard chemotherapy was given to patients with this genetic profile, fewer than 5% had no signs of cancer after surgery, UCL said. Over the next few years, the trial will also assess overall survival and relapse rates. The approach also meant patients did not require any post-operative chemotherapy, which has side effects and is tough to endure. Dr Kai-Keen Shiu, the trial’s chief investigator and a consultant medical oncologist at UCLH, said: “Our results indicate that pembrolizumab is a safe and highly effective treatment to improve outcomes in patients with high-risk bowel cancers, increasing the chances of curing the disease at an early stage.” Shiu cautioned that the team would need to wait to see whether the patients in the trial remained cancer-free over a longer period of time, but said the initial indications were “extremely positive”. “Immunotherapy can make tumours disappear before surgery. If you melt the cancer away before surgery you normally triple survival chances,” Shiu added. “If patients have a complete response to pembrolizumab it can triple your chance of survival. “Patients also don’t need any chemotherapy after so they avoid all those side effects.” Dr Marnix Jansen, a clinician scientist at the UCL Cancer Institute, said more work needed to be done to assess pembrolizumab before it could be considered standard treatment. “But given the quality of the outcomes in this trial I think it’s possible that we could see it in the clinic within a couple of years if subsequent trials are similarly successful.”